Influence of the granulation step on pellets prepared by extrusion/spheronization

Pellets were prepared by granulation/extrusion/spheronization. Four different procedures applying different amounts of shear were used for granulation: planetary mixer, high-shear mixer and twin-screw extruder with two different screw assemblies. Extrusion was performed on a rotary ring die press. Pellet properties were rated by size, shape, release behaviour and different mechanical characteristics like crushing strength or porosity. The study revealed that different granulation methods affected pellet properties by the application of different shear forces. The application of higher shear forces during granulation resulted in a higher water content necessary for successful pelletization. This finding is in contrast to conventional granulation and was explained by the crystallite-gel-model. The difference in water content of the extrudate influenced the extent of shrinking during drying, which was responsible for the different mechanical characteristics of the pellets. The release rate for paracetamol was higher for pellets with lower porosity. This is explained by the presence of drug crystals on the surface of these pellets due to the higher extent of shrinking during drying.